Coil system more particularly intermediate-frequency band-pass filters



Aug. 26, 1958 v VERHCEVEN 2,849,690

COIL SYSTEM MORE PARTICULARLY INTERMEDIATE-FREQUENCY BAND-PASS FILTERS Filed Dec. 12, 1955 INVENTOR LAMBERTUS VERHOEVEN AGENT 2,849,690 Patented Aug. 26, 1958 COIL SYSTEM MORE PARTICULARLY INTER- MEDIATE-FREQUEN CY BAND-PASS FILTERS Lambertus Verhoeven, Eindhoven, Netherlands, assignor,

by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application December 12, 1955, Serial N 0. 552,568

Claims priority, application Netherlands December 21, 1954 4 Claims. (Cl. 336-75) This invention relates to high-frequency coil systems comprising two coils of adjustable inductance, which coils are housed parallel to one another in a common screening envelope and the coupling of which is variable. The invention also relates more particularly to intermediate-frequency band-pass filters.

It is already known that the screening envelope or conductive shield brings about a certain coupling between the coils, which coupling may be varied, for example by providing an apertures in the wall of the envelope and filling the aperture with conductive material to a greater or lesser extent. However this is a complicated method which also detrimentally affects the screening action.

The coupling between two parallel coils may, as a rule, alternatively be varied by means of a movable closed loop (so-called link) which embraces the two coils. The application thereof in a screened coil system involves the disadvantage that the loop inside the screening envelope can vary but slightly the fairly strong coupling which is already brought about by the envelope.

The object of the invention is to provide an inexpensive construction for a coil system of the aforementioned kind, in which the said disadvantage is suppressed and the coupling may easily be varied.

According to the invention, inside the screening envelope or housing, a metal plate extending substantially at right angles to the axes of the coils is arranged to be movable in the axial direction of the coils, the plate having a recess in the form of two apertures which allow passage of the coils with some clearance and which are interconnected by a narrower portion of the recess.

In order that the invention may be readily carried into effect, it will now be described, by way of example, with reference to the accompanying drawing, showing one embodiment in vertical section (Fig. 1) and in horizontal section (Fig. 2).

Fig. 1 shows an intermediate frequency band-pass filter comprising two parallel coils 1 and '3, which may be mounted in the vertical position on a horizontal chassis plate 7 by means of an insulating base 5, for example of synthetic resin, to which the coils 1 and 3 are secured. The coils are housed in a metallic screening envelope or shield 9, for example, of aluminum, likewise secured to the base 5 and the lower side of which is open, while in the opposing wall (that is, to say the upper wall) two apertures 11 and 13 are provided to allow passage of an adjusting tool. By means of this toolfor example a screwdriver of insulating material-it is possible for two threaded magnetic cores 15 and 17, for example of powdered iron, within the coils 1 and 3, to be displaced for regulating the self-inductances of the coils.

A metal plate 19, for example of brass, having rectangularly bent edges or flanges, which plate is substantially at right angles to the axes of the coils and has a recess, is arranged to be movable in the envelope 9 for adjusting the coupling between or mutual inductance of the coils. The recess in the plate 19 has the shape of two-in this case circular-apertures 21 and 23, which surround the coils 1 and 3, preferably concentrically, with some spacing and which are interconnected by means of a narrower slot-shaped portion 25. The recess has the function of a closed (double) coupling loop which surrounds the two coils and couples them according to known principles. The coupling loop actually comprises two single loops (21 and 23) whichdue to the narrow portion 25-embrace.

the coils 1 and 3 as completely as possible and hence are strongly coupled with them. It has thus been found possible for the coupling already provided by the metal envelope 9 to be increased by a considerable (adjustable) amount without the edges of the apertures 21 and 23 embracing the coils 1 and 3 so tightly that contact and dam age to the coils and their supply leads from the side of the plate 19 might occur.

The bent edges of the plate 19 resiliently engage the inner side of the envelope -9, so that under normal conditions the plate, after adjustment, is fixed in position without taking further steps. The plate 19 may be displaced without preliminary removal of the screening envelope 9 by means of a tool 27 (shown in phantom in Fig. l) in the form of a small table-like member having at least three and in this case four legs of insulating material, which maybe passed through four small apertures 29 in the upper wall of the envelope 9. The plate 19 can be moved downwards by this tool till the desired coupling has been reached. If during this movement one has passed beyond the proper adjustment it'is possible for the plate, after the envelope has been removed, to be slightly moved back and the adjustment to be repeated. After some experience, one usually readily succeeds in adjusting the coupling definitely without removal of the screening envelope.

If desired, the brass plate 19 may be fixed at the adjusted position by providing, at each side of the envelope 9, a drop of solder 31 to adhere to the bent edge of the brass plate 19 through one of a plurality of apertures 33 in the side-wall of the aluminum envelope 9.

What is claimed is:

l. A coil system adapted for high frequency operation, comprising a pair of substantially parallel, spaced coils having longitudinal axes, a common conductive housing for said coils, and means for adjusting the coupling between the coils, said adjusting means including a conductive plate-like member mounted wholly within the housing and extending substantially at right angles to the axes of the coils, said plate-like member having a pair of apertures therein each larger than one of said coils and each accommodating one of said coils, whereby each of the coils is spaced from the portions of the conductive member defining their respective aperture, said conductive member also having a further aperture of smaller width than each of said pair of apertures and interconnecting these apertures, said plate-like member having been moved in an axial direction to a position within the housing at which the desired coupling between the coils is obtained.

2. A coil system adapted for high frequency operation, comprising a pair of substantially parallel, spaced coils having longitudinal axes, a common conductive housing closely surrounding said coils, and means for adjusting the coupling between the coils, said adjusting means including a metal plate mounted wholly within the housing and extending substantially at right angles to the axes of the coils, said metal plate having two spaced apertures and a narrow slot therebetween communicating with said apertures, said apertures accommodating said coils and being larger than the coils whereby the metal plate defines an annular space with each of the coils, said housing having a small aperture providing access to the metal plate axially to move same to obtain a desired coupling between the coils.

3. A coil system adapted for high frequency operation, comprising a pair of substantially parallel, spaced coils having longitudinal axes, a common metal housing closely surrounding said coils, and means for adjusting the coupling between the coils, said adjusting means including a metal plate having a flanged portion and mounted within the housing and extending substantially at right angles to the axes of the coils and with the flanged portion engaging the housing, said metal plate having two, spaced, substantially circular apertures and a narrow slot therebetween communicating with both apertures, said apertures concentrically accommodating said coils and being larger than the coils whereby the metal plate defines an annular 4 space with each of the coils, said metal plate occupying a position within the housing 'at which a desired coupling between the coils is obtained.

4. A coil system as set forth in claim 3 wherein one wall of the housing extending parallel to the metal plate has a plurality of small apertures therein to enable access to the metal plate for adjusting purposes.

References Cited in the file of this patent UNITED STATES PATENTS 2,388,295 Shea Nov. 6, 1945 FOREIGN PATENTS 124,905 Australia July 17, 1947 

